1975 Johnson 50hp motor troubles

[Starcraft Tony]

I've got a quick question for the pros that will hopefully save me a lot of exploring/reading/money. This afternoon I took the boat out for a quick blast. Boat started fine and has been running good for the last few months. Running arcoss the bay at WOT the motor just died, almost like running out of gas, but without the sputtering. I turn to see whats going on and thats when I see a little bit of smoke coming out of the engine (1975 50hp johnson). The hot light or alarm did not sound so i'm assuming that needs repair as well. Anyways couldnt get it started so I fired up the trolling motor and got her home. Now I know I have a whole service manual of things to check but I'm looking for some quick advice. I'm not real mechanically inclined but when I started looking around this is the first thing I noticed . I'm not positive but I dont think the starter motor should not be engaged without being cranked right? So here is my hopefully easy/cheap fix stab in the dark guess of what might of happened here. Could the starter motor have engaged in the flywheel during WOT and burned up (causing the smoke)?

 

[tashasdaddy]

Re: 1975 Johnson 50hp motor troubles

that probably have happened when trying to restart, ususally cause by a weak battery or poor battery cables or connections.

 

[Starcraft Tony]

Re: 1975 Johnson 50hp motor troubles

I got to work on the motor for a few hours after work today, and so far this is where I'm at.

tashasdaddy: charged the battery, cut off the old terminal ends and replaced with some new marine ones as they were pretty nasty (cleaned terminals first). After screwing with the starter motor the starter disengaged and now when I crank it, it goes up and down pretty good. Thanks for the input.

1) Checked plugs for spark - spark on both plugs - replaced with new plugs
2) Checked fuel filter - pumped bulb and it squirts fuel - pretty sure this means its workin.
3) Checked compression - reads 50 on both cylinders. Last May this motor had compression of 100+ at both cylinders.

Anybody have any suggestions on what I broke that would cause both cylinders to loose half their compression?

 

[tashasdaddy]

Re: 1975 Johnson 50hp motor troubles

retest compression, read here http://forums.iboats.com/showthread.php?t=299680 if the same i would suspect head gasket first. 50 ain't good.

 

[Starcraft Tony]

Re: 1975 Johnson 50hp motor troubles

Finally will have some time to work on this motor tomorrow

tashasdaddy: Retested compression and got the same results.

Before I get into the head gasket, can somebody please help me identify what this is/was (melted wire). I've looked through the manual but cant find it. . Just want to make sure this is not the casue of all my problems.

Thanks

 

[Daviet]

Re: 1975 Johnson 50hp motor troubles

Kinda looks like a temp sender.

 

[tashasdaddy]

Re: 1975 Johnson 50hp motor troubles

that is the temp sender to the alarm. definately overheated. hopefully only head gasket, if that is it, while there ,remove water jacket, clean, new gasket, replace tstat, and impeller. cleaning the cooling system is a lot easier at this point.

impeller water pump.>> http://www.iboats.com/mall/partfind...gd_poid=110954&gd_row=28&**********=566071645

tstat Kit 18-3674

head gasket >> http://www.iboats.com/Sierra_18_295...3958477--**********.566071645--view_id.173752


water jacket gasket >> http://www.iboats.com/Sierra_18_094...3958477--**********.566071645--view_id.173862

BRP part 0386686 TERMPERATURE SWITCH 1 $68.45 USD

 

[DGartzos]

Re: 1975 Johnson 50hp motor troubles

These are outstanding cooking skills!!! That is how i like my stake done, rare!!!

Last year, had my buzzer salted solid, it just managed a well hidden burp. Coming into the bay, late at night, got a plastic bag folded on the leg shutting both water inlets. Couldn't hear nothing until engine started loosing power. Killed it and opened it to see the thermostat plastic cup and temp sender melting out the head. Well, managed to push in what was left of that cup without springs and thermostats and did get home.

So good cooking skills are important to boaters!!!

Always hear a crispy and loud buzzer test when turning the key on !!!

 

[5150abf]

Re: 1975 Johnson 50hp motor troubles

Had a buddy that did that, actually his brother who likes beer,ALOT.

Got stuck in the mud and just kept on the gas, he got it so hot it actually melted the pressure relief valve, it was in 3 blobs at the bottom of the water jacket.

Changed the head gasket and sanded the head flat and it got 150psi when I was done so he really lucked out.

Take piece of 400 grit sand paper and a piece of glass and sand the head till there are sand marks across the entire surface.

Hope it works out for you.

 

[Starcraft Tony]

Re: 1975 Johnson 50hp motor troubles

Finally got a chance to work on the motor this past weekend.
1) Removed cylinder cover and cleaned off what was left of the gasket
2) Removed cylinder head, Head gasket had a hole in the middle (between the two cylinders). Both pistons look great, bottom cylinder walls smooth as can be, top cylinder only has a slight scratch.
3) Cleaned cylinder head installed new head gasket, temp switch, thermostat. Torqued bolts to specs.
4) Installed new cylinder cover gasket, then cover, and torqued bolts to specs.
5) Removed lower unit gear case to check water pump ( i had this replaced 1.5 seasons ago) visual inspection I thought this pump looked fine.
6) Opened water pump and impeller looks fine. Replaced it anyway.
7) Reinstalled lower unit gear case (disconnecting and reconnecting the shift rod is real fun for extra large and fat hands)

After all of this I was feeling not so good as I thought the impeller failed thus causing the overheat but no such luck. Ran a compression test and again got 50 on both cylinders. So as you all can imagine I was pretty dissapointed. So what else should I be checking guys?

 

[DGartzos]

Re: 1975 Johnson 50hp motor troubles

reading 50 both cylinders is much better than reading 125 on one and 50 on the other, then you really have trouble ...

- you sure gauge OK? any chance to test with another,
- is it mounted air tight?
- battery fully charged?
- throttle open?
- slightly preoil cylinders?

otherwise doesn't sound too good

 

[Starcraft Tony]

Re: 1975 Johnson 50hp motor troubles

One thing I forgot to mention. When got down to the cylinder head I could see that the tstat was fried, but in the hole next to the tstat location the book refers to it as "pressure relief componants". I could not see anything melted in this hole; in fact I worked it with a screwdriver and it seems solid all around. So my question is, does this year of motor have "pressure relief componants", and if so could my not replacing it still be giving me the compression problems?

Thanks.

 

[bktheking]

Re: 1975 Johnson 50hp motor troubles

First of all have you tried another gauge? Is yours a screw in type with o rings or one of those hold it and crank it ones?

 

[Daviet]

Re: 1975 Johnson 50hp motor troubles

Are the cylinders dry? See if it will start and then recheck your compression.

 

[Starcraft Tony]

Re: 1975 Johnson 50hp motor troubles

Bought a new compression gauge and retested the motor (screw in type with O rings, old one was the same style). This gauage is reading approx 80 on both cylinders (top cylinder is actually just shy of 80). Better then 50 but still not where it should be ( tested 100 on both cylinders last May). I have tested the compression both dry and wet (wet when originally reassembled).

Daviet " Are the cylinders dry? See if it will start and then recheck your compression. " At this time I am unable to get the motor started.

Another thing I noticed today when checking compression is the prop spinning with the flywheel in both fwd and netural. Now I'm pretty green when it comes to repairing outboards, but I am pretty sure this is not supposed to happen. I'm assuming I screwed something up when removing the lower gear case to check the water pump, I just dont know what. I followed the manuals directions step for step and even spun the flywheel as the lower was being reattached. Everything went really smooth so I assumend I did everything corretly, but I guess I was wrong. So help me out please, what did I do here?

Thanks,

 

[Starcraft Tony]

Re: 1975 Johnson 50hp motor troubles

Any ideas? I gotta try and get this thing fixed for the holiday weekend.

 

[Daviet]

Re: 1975 Johnson 50hp motor troubles

The things necessary for an engine to run is, compression, spark, fuel and correct timing. You have compression, a little weak but it should at least pop. You said that you have good spark. Timing should not be an issue by the way you explained repairs, you did not remove the flywheel and mess around under there. Remove jet plugs and see if there is fuel in the carb bowels, pump primer bulb with screws out and watch fuel flow, could be messy. If bowels do not have fuel and will not flow fuel when bulb is squeezed, needle and seats in carbs might be stuck. If there is fuel flow, squirt some fuel mixture into carbs and see if it will try and start. If it tries to start but will not run without squirting fuel mix into carb you have carb problems. Remove carbs and rebuild. Battery needsn to be fully charged when testing.

 

[Starcraft Tony]

Re: 1975 Johnson 50hp motor troubles

Thanks Daviet, I'll give that a try tomorrow, but I have a few rookie questions if you dont mind.
1) Could I have screwed something up in the carbs when the engine overheated?
2) You seem pretty experieced, do you maybe know what I did to the lower unit?

Thanks for the help

 

[Daviet]

Re: 1975 Johnson 50hp motor troubles

I don't think you could damage the carb by overheating, short of a meltdown. When you had the lower unit off, did you spin the shift shaft, questioning the lenth getting changed. Without the engine running can you spin the prop? What do you mean when you say,prop spinning with flywheel in forward and neutral?

 

[Starcraft Tony]

Re: 1975 Johnson 50hp motor troubles

Forgive my ignorance for this is my first attempt at working on outboards. I disconnected the shift rod from under the starter as directed by the manual to remove the lower. When reinstalling all I did was spin the flywheel (as directed by the book). From that point everything lined up exactly as i took it off, all i had to do with the shift rod was line it up between the holes and insert the bolt.

To answer your question though, i cannot spin the prop without the engine running (pretty sure I could spin the prop before when the boat was off and in netural). I had a helper crank the engine during my last compression test and noticed the prop spinning as the engine was cranking. I told my helper to put the boat in netural and he said it was, I then confirmed that it was in netural, craked it up again and the watched the same results.

Thanks for all the help